As is commonly known, a mobile radio communication system adopting a CDMA system has recently received attention. This system introduces a spread spectrum communication system as a communication system.
Prior art mobile radio terminal equipment of the above mobile radio communication system will now be described with reference to FIG. 1. The equipment will be explained here with a particular emphasis on a receiving system according to the present invention.
In a transmitter device 12, transmission data such as digitized voice and data is modulated by a digital modulation method such as PSK modulation, and the modulated data is converted into a wideband baseband signal using a spreading code. The spread signal is then up-converted into a radio-frequency signal and input to a first antenna 10 through a shared unit 11. The above signal is radiated from the first antenna 10 into space and transmitted toward a base station not shown.
A radio signal transmitted from the above base station is received by the first antenna 10 and input to a receiver device 13 through the shared unit 11. The receiver device 13 includes a radio circuit 14, an intermediate-frequency circuit 15, and a Rake receiver 16.
First, in the radio circuit 14, a radio signal received from the shared unit 11 is input to an attenuator 14a and attenuated herein by a preset amount. The signal passing through the attenuator 14a is amplified to a predetermined level by an amplifier 14b and then mixed with a signal, which is generated by a frequency synthesizer 14d, by a mixer 14c. The mixed signal is down-converted into an intermediate-frequency signal.
The intermediate-frequency signal is input to the intermediate-frequency circuit 15 and amplified to a predetermined level by the amplifier 15a. The amplification result only in a desired band passes through a band-pass filter (BPF) 15b and is mixed with a signal, which is generated by a frequency synthesizer 15d, by a mixer 15c. The mixed signal is converted into a baseband signal, and the baseband signal is converted into a digital signal by an A/D converter (A/D) 15e and input to the Rake receiver 16.
The Rake receiver 16 includes a searcher 16a, fingers 16b, 16c and 16d, and a symbol synthesizer 16e, and the above digital signal is input to the searcher 16a and the fingers 16b, 16c and 16d. 
The searcher 16a detects signals coming to its own terminal from the base station through a plurality of routes, i.e., a so-called multipath, and de-spreads them using the same spreading code as used for spreading on the transmitter side. Then, Ec/Io (Io indicates energy of all received signals and Ec represents a signal level of a desired wave) is obtained for each of de-spreading effects, and a delay time difference (a delay profile) between them is obtained. Based on these, reception timing (de-spreading timing) of the multipath is determined and assigned to the fingers 16b, 16c and 16d. 
The fingers 16b, 16c and 16d de-spread the above digital signal using the same spreading code as used for spreading on the transmitter side at the de-spreading timing assigned by the searcher 16a. 
The symbol synthesizer 16e synthesizes the symbols of multipath components de-spread by the fingers 16b, 16c and 16d in consideration of the de-spreading timing assigned to each of the fingers 16b, 16c and 16d. 
The signal having a symbol synthesized by the symbol synthesizer 16e is demodulated in a signal processing section 17 in the post-stage in accordance with the digital modulation on the transmitter side, and reception data is reproduced accordingly.
Further, in the mobile radio terminal equipment, a control section, not shown, performs control for a handoff in accordance with the Ec/Io of a pilot signal obtained by the searcher 16a. 
When a signal is received intermittently in a standby state, the control section measures Ec/Io of a pilot signal from another base station to perform a handoff if the following conditions are satisfied: (1) the above Ec/Io becomes lower than a prescribed value; (2) the Ec/Io becomes the prescribed value lower than that in the last reception; and (3) a difference in Ec/Io between adjacent base stations falls within the prescribed value. When the Ec/Io of the pilot signal from another base station is larger than the prescribed value, a handoff is performed for another base station.
In a call state of the mobile radio terminal equipment, when Ec/Io of a pilot signal of a base station currently connected thereto becomes lower than the prescribed value and Ec/Io of a pilot signal of an adjacent base station becomes larger than the prescribed value, a handoff is carried out while communicating with a plurality of base stations including a base station satisfying a given condition.
However, the multipath resolution of the searcher 16a is a reciprocal of a chip rate in the prior art CDMA system mobile radio terminal equipment. If, therefore, a delay time of the multipath is smaller than the reciprocal, the multipath components are separated in the fingers 16b, 16c and 16d as described above and thus the symbols thereof cannot be synthesized.
In other words, if the delay time of the multipath is short, there occurs a problem in which Rake reception cannot be performed and a phasing-resistant property is decreased to make it impossible to secure a stable communication quality. The problem is caused in low-speed movement such as a walk and in a stationary state more markedly than in high-speed movement.
If, under the above circumstances where no Rake reception can be performed because of a short delay time of multipath, multipath phasing occurs to make Ec/Io of a pilot signal from the current base station lower than a prescribed value even for the time being, processing for a handoff will be started.
Since the Rake reception cannot be carried out depending on conditions for which the above phasing occurs, a handoff will be performed for a distant base station though the current base station is nearer at hand. Since, in this case, a sufficient signal level cannot be obtained stably from the base station after the handoff, a phenomenon occurs in which a handoff is performed again for the base station before the handoff.
Such a useless operation remarkably consumes a battery current. Even though a handoff is not performed after all, it is necessary to search for a base station for a handoff in response to a pilot signal from another base station in order to determine whether the handoff is performed or not; accordingly, the same problem of uselessly consuming a battery current occurs.
In the CDMA system, Ec/Io of a signal from each base station cannot be specified until the respective sections in RF, IF and BB bands are operated for comparison of the Ec/Io; therefore, the power consumption becomes higher and the above problem becomes more serious than in another system such as a PDC (Personal Digital Cellar) system in which an RSSI unit measures the strength of a signal received from each base station.